Infrared spectroscopic study on the properties of the anhydrous form II oftrehalose. Implications for the functional mechanism of trehalose as a biostabilizer

FTIR spectra were obtained for several different states of trehalose includ ing dihydrate crystal, anhydrous form II (designated by Gil, A. M.; Belton, P. S.; Felix V. Spectrochim. Acta 1996, A52, 1649-1659), anhydrate crystal , dried melt, amorphous solid and aqueous solution. From the observation of the symmetric and antisymmetric stretch vibrations of the glycosidic linka ge, it is found that this sugar assumes at least three types of backbone co nformations. Among them, the conformation with C-2 symmetry is characterize d as 'open state', which means that the sugar easily absorbs water molecule s. The conformation of the sugars in anhydrous form II and in freeze-dried trehalose is shown to be in the open state. Next, the hygroscopic propertie s of the anhydrate, form II and the amorphous solid are compared based on t heir IR spectra. Interestingly, form II alone is converted to the original dihydrate in a week under mild environmental-like conditions: relative humi dity of 40% and room temperature. These results suggest the possibility tha t form II plays a role in avoiding the devitrification of the sugar glass. Finally, we discuss the role of form II in preserving freeze-dried biomater ials. (C) 2001 Elsevier Science Ltd. All rights reserved.